The present invention relates, in general, to a method for the preparation of a clay-dispersed polymer nanocomposite and, more particularly, to the use of an oxygen atom-carrying polymer with thermodynamical compatibility with a binder resin in preparing a clay-dispersed polymer nanocomposite, thus delaminating clay completely to silicate lamellas.
With the aim of overcoming limited physical properties of general-purpose plastics, the techniques for preparing clay-dispersed organic/inorganic composites are characterized in that clay ores of silicate layered structures are delaminated into silicate layers at nano levels and the silicate layers are dispersed in polymer resins, thereby upgrading general-purpose plastics to engineering plastics. Silicate layer, a structural unit of clay, is however difficult to disperse in polymer resins owing to its strong van der Waals attraction. To circumvent this problem, intercalants are suggested. According to a compounding technique, for example, an intercalant with a low molecular weight is introduced into the silicate layered structure to aid the penetration of polymer resins into the structure, thereby delaminating clay ores and dispersing the silicate layers in the resins.
However, the conventional compounding technique has such a problem that, when nanocomposites are prepared from some resins, including poly(styrene-co-acrylonitrile)copolymer resins, poly(acrylonitrile-co-butadiene-co-styrene) copolymer resins, and poly(vinylchloride) resins, it is virtually impossible to completely delaminate clay ores to the extent of a silicate layer, which is a structural unit of clay. In the nanocomposites of such resins, prepared by the conventional compounding technique, in fact, there are observed blocks of nano scales, which result from the aggregation of several to tens silicate lamellas [see, Korea Polymer Journal, 7, 310 (1999); ibid, 8, 95 (2000); ibid, 8, 120 (2000)]. The reason is that a nitrogen and a chlorine atom, which are contained in the repeating unit acrylonitrile of poly(styrene-co-acrylonitrile) or poly(acrylonitrile-co-butadiene-co-styrene) copolymer resins and the repeating unit vinyl chloride of poly(vinylchloride) resin, respectively, is smaller in electronegativity than is an oxygen atom, which is present within organophilic clay, so that it is not easy for the polymer chain to penetrate between silicate layers.
Leading to the present invention, the intensive and thorough research on the preparation of clay-dispersed polymer nanocomposites, conducted by the present inventors, resulted in the finding that a polymer carrying oxygen atoms can itself penetrate into silicate structures and, when constituting a matrix for the composites, along with other polymers, help penetrate the binder resins into layered structure of silicates if they are thermodynamically compatible with the oxygen-carrying polymer.
Therefore, it is an object of the present invention to overcome the above problems encountered in prior arts and to provide a method for the preparation of clay-dispersed polymer nanocomposites, in which clay ores are completely delaminated to a silicate layer, which is a constituent minimum unit.
Based on the present invention, the object could be accomplished by a provision of a method for preparing a clay-dispersed polymer nanocomposite, which comprises introducing an oxygen-carrying polymer, alone or in combination with a thermodynamically compatible resin, as a matrix resin.